1. Technical Field
The present invention relates to an ionic conductive organic electrolyte and an ionic conductive polymer electrolyte.
2. Description of Related Art
Advances in electronics have allowed the performances of electronic devices to be enhanced, and electronic devices have been miniaturized and made portable. Accordingly, secondary batteries with high energy density have been needed as power sources for such devices. In response to such need, nonaqueous electrolyte system secondary batteries with significantly enhanced energy density, i.e., lithium ion secondary batteries with organic electrolytic solution (hereafter simply referred to as “lithium batteries”), have been developed, and they have become widely prevalent in recent years. Lithium batteries use, for example, lithium metal complex oxides such as lithium-cobalt complex oxides as positive electrode active materials. They primarily use as their negative electrode active materials multilayered carbon materials capable of intercalating lithium ions in the layered structure (formation of lithium intercalation compounds) and deintercalating lithium ions out of the layered structure.
Lithium batteries use a combustible organic electrolytic solution. Thus, securing of safety in the case of overuse, such as overcharge or over-discharge, is becoming difficult with the enhancement in energy density of the batteries. Accordingly, lithium polymer batteries in which the combustible organic electrolytic solution has been replaced with a solid lithium-ionic conductive polymer were developed.
A mechanism of an ionic conductive polymer for conducting ions that has heretofore been examined is known to occur in conjunction with the motion of a polymer molecular chain. Ionic conductivity is governed by mobility of the molecular chain and by motion of a molecular chain having high activation energy, which is required for segmental motion. Thus, ionic conductivity at room temperature is approximately 10−4 Scm−1, but it becomes significantly lower as the temperature drops.
The present inventors conceived of the application of single bond rotation with low activation energy to a mechanism for conducting ions that is not governed by motion of a molecular chain.
An organic group having a functional group, which is a ligand coordinated to a lithium ion, is bonded to another organic group through a single bond, and thus, free rotation can be realized in a wide temperature range. This rotation allows lithium ion exchange between adjacent similar functional groups, and ions are conducted via such exchange. This mechanism of conducting ions has allowed realization of the preparation of a polymer electrolyte having excellent temperature dependence (JP Patent Publication (Kokai) No. 2004-6273 A).